This invention relates to an integrated circuit and more particularly, a 4-bit by 2-bit integrated circuit cell which can be arranged in a multiplier array.
The use of Booth's approach of multiplication by using the sequence of multiplier bits to control the digital multiplication routine is known. The order of binary 0's and binary 1's of the multiplier controls either the addition or subtraction of the multiplicand or the addition or subtraction zeros to the accumulated partial product. After each addition and subtraction, the results are shifted 1 bit to the right. This technique is extremely useful because it allows for complement two's multiplication.
Modified basic multiplier cells using this algorithm are possible, and moreover it can be extended to larger grouping of multiplier bits for more efficient multiplier cell configurations. This data maniputation only allows for the examination of two bits at any single point in time, however it can be extended to any number of adjacent bits and is referred to in the art as multiplier coding. In order to facilitate a 4-bit by 2-bit cell, three adjacent bits must be examined using quaternary data processing techniques. The truth table for the quaternary algorithm is as follows:
______________________________________ Multiplier Bits Y.sub.1 Y.sub.0 Y.sub.-1 Operation ______________________________________ 0 0 0 Add zero 0 0 1 Add multiplicand 0 1 0 Add multiplicand 0 1 1 Add 2 .times. multiplicand 1 0 0 Subtract 2 .times. multiplicand 1 0 1 Subtract multiplicand 1 1 0 Subtract multiplicand 1 1 1 Subtract zero ______________________________________
The present invention decreases propagation delay time by implementing the 4-bit multiplier array in accordance with these known multiplying techniques by employing a current switch emitter follower type logic gate that allows an inverted carry signal to be passed directly to its adjacent cell internal to the array. External carry signals received by the least significant device in the array are inverted prior to processing within the cell array.